Headcanon: Jumin has a will because he could be easily assassinated. In his will, Elizabeth the 3rd gets everything except things that can only be run by humans (ex: The company, his house, his money...) In that case, those things are given to Jaehee because he knows she'll take care and be responsible of them. Other than that, everything else goes to Elizabeth the 3rd.

Also

Areum X Gyeong is Elizabeth X long cat human form and nobody can tell me otherwise.